Plasma vitellogenin (Vg) concentration is the most commonly used biomarker for assessing the estrogenic potency of endocrine disrupters (EDs). However, this protein is not always induced in fish subjected to realistic exposure scenarios. Therefore the value of investigating the compromise of other physiological processes to develop alternative biomarkers is readily evident. To address this issue individually tagged rainbow trout were given different doses of 17b-estradiol (E2) or atrazine (A), through a single injection, or exposed to waterborne pulses of 4-nonylphenol (NP) or atrazine. Endocrine responses were monitored by measuring plasma Vg and sex steroid concentrations.
Individual specific growth rates (SGR) were recorded and white muscle total protein, RNA and DNA concentrations were measured as biochemical growth indices. In addition liver catalase (CAT) activity and metallothionein (MT) concentrations were assessed. The effects of these agents on growth were dose dependent. For all three compounds the highest doses resulted in a linear relationship between SGR and white muscle cell size (RNA:DNA ratio), suggesting an increased contribution of growth through hypertrophy in ED-exposed fish. Vg was induced in fish injected with 0.5 mg/kg E2 suggesting these responses are related to endocrine disruption. CAT activity increased in fish 5 days after a 2-h exposure to 0.5 mg/l waterborne atrazine, whereas 10 days after exposure the trout showed reduced CAT activity. A 2-h water exposure to 15 ı`g/l NP resulted in reduced MT levels. Nevertheless A and NP as known estrogen-inducers failed to increase vitellogenin synthesis, suggesting CAT and MT to be more sensitive responses. Supported by the European Commission’s fellowship 15708-2000-02 P1B20 ISP IT and the European Union’s Marie Curie Grant EVK1-CT-2002-57003.